Elm Notes

notes.elm

-- JSON decoding

import Json.Decode

type alias Document = { message : String }

-- a decoder of type String that decodes the "message" field
message = Json.Decode.field "message" Json.Decode.string
-- a decode of type Document
doc = Json.Decode.map Document message
-- parses the provided String into a Document
Json.Decode.decodeString doc "{\"message\":\"stuff\"}"

-- decoding JSON into a record with a Maybe (when the field is mandatory in the JSON)

type alias Document = { message : Maybe String }
decoder = map (\msg -> Document Just msg) (field "message" string)

-- decoding a List of JSON

documentDecoder = map Document (field "message" string)
documentsDecoder = list documentDecoder

-- Anonymous function with multiple arguments
f = \a b -> a + b

-- Boolean not is a function: Bool -> Bool
-- to negate the results of another Bool-returning function, compose it with not

lt10 x = x < 10
gte10 = List.filter (lessThan10 >> not) [2,4,6,8,10,12]